By using optical shape sensing, the shape of an elongated object, e.g. a steerable medical device, can be reconstructed by integration of an optical fiber with optical shape sensing elements in such a device. This is possible by optical interrogating the optical fiber e.g. with optical shape sensing elements by means of Fiber Bragg Gratings or Rayleigh based elements. A real time visualization of the reconstructed 3D shape has a number of applications, e.g. medical applications, since it allows important navigational guidance for elongated interventional medical devices. Such devices can be used for example within medical applications in the form of diagnostic and navigation devices, e.g. catheters, guide wires, endoscopes, stylets or needles, and treatment devices, e.g. ablation devices.
In practical implementations, optical shape sensing is possible with an acceptable degree of accuracy up to a length of 1.5-2 meters. However, the optical fiber itself can be several meters long. For some applications, this length limitation is undesired. This limitation can be mitigated by using two separate optical shape sensing devices being tracked with respect to their position in one X-ray image. However, this is unpractical since it requires extra work, and accuracy may be compromised. Further, for some applications such two optical shape sensing devices can be too far apart for such method to work.
WO 2012/168855 A1 discloses a system for monitoring changes during therapy and includes first and second probing segments with optical fiber sensor disposed therein. The second segment is generally disposed apart from the first probe and provides a spatial reference point for the first segment. The first and second segments have at least one common position to function as a reference between the first and second probes.
US 2011/0098533 A1 discloses a medical instrument including a distortion probe disposed in an insertion portion to be inserted into the interior of an examinee provided with a plurality of FBG sensor sections that detect distortion of the insertion portion, and a coordinate calculation section that calculates first three-dimensional coordinates of the respective FBG sensor sections according to a first three-dimensional coordinate system.